The present invention relates to an electrically conductive ceramics suited for use in electrodes, heaters, semiconductor-related parts such as ionizers, wafer transporting hands, chamber domes, clamp rings, and other parts of a semiconductor manufacturing machine, and to a process of producing such a ceramics. More particularly, the invention relates to an electrically conductive ceramics suitable for use in parts of a plasma etching apparatus, for example, which is used in a severe environment such as a plasma environment or a high-temperature oxidizing atmosphere, a process of producing such a ceramics, and an electrostatic chuck using the conductive ceramics as a dielectric layer thereof.
Conventional conductive ceramics include those which consist of a single substance showing electrical conductivity, such as SiC, TiN, TiC, WC, WO2, and TiO2xe2x88x92x (0 less than x less than 2) (titania with oxygen deficiency). Composite ceramics, such as Al2O3xe2x80x94SiC, Al2O3xe2x80x94TiO2xe2x88x92x (0 less than x less than 2), AlNxe2x80x94TiN(TiC) and Si3N4xe2x80x94TiC(TiN), are also available which are each a mixture of an insulating ceramics and a conductive ceramics and of which the mixing ratio of the ceramics can be varied to change the electrical conductivity.
Where electrically conductive ceramics are used in the applications mentioned above, their electrical conductivity should desirably be changed to meet the purpose. However, in the case of ceramics which consist of a single substance showing electrical conductivity, among those mentioned above, it is difficult to control the electrical conductivity.
On the other hand, in the case of composite ceramics obtained by mixing an insulating ceramics with a conductive ceramics, the electrical conductivity can be changed by varying the proportion of the conductive ceramics. However, the electrical conductivity shows a steep change and thus is subject to variations, making it difficult to control the electrical conductivity to a desired value. Especially in cases where a composite ceramics is used for a long time in a severe environment as mentioned above, an additional problem arises in that the electrical conductivity gradually varies.
Meanwhile, an electrostatic chuck is used in a semiconductor manufacturing machine etc. as a jig for fixing, straightening, or transporting silicon wafers or the like. The electrostatic chuck has a dielectric layer provided on its electrode and is constructed such that, when a voltage is applied to the electrode, the dielectric layer electrostatically attracts a wafer thereon.
As the dielectric layer of such an electrostatic chuck, alumina, sapphire, etc. having an electrical conductivity of 10xe2x88x9215 S/cm or less are conventionally used. However, where a material with high insulation quality, such as alumina, is used as the dielectric layer of an electrostatic chuck, attraction is achieved by means of an electrostatic attractive force (Coulomb force) produced between the electrode and the electric charge induced in an object to be attracted. Accordingly, to obtain large attractive force, the thickness of the dielectric layer must be reduced to 0.1 mm or less, which, however, increases the possibility of the dielectric layer being broken during machining.
Attempts have therefore been made to obtain large attractive force without the need to form a thin dielectric layer, more specifically, to enhance the electrostatic attractive force by admixing a dielectric material such as alumina with the aforementioned conductive ceramics to increase the electrical conductivity of the dielectric layer (Up to 10xe2x88x928 to 10xe2x88x9214 S/cm) and thereby permit movement of the electric charge. Namely, by thus increasing the electrical conductivity of the dielectric layer, it is possible to induce electric charge at the surface of the dielectric material, and since electrostatic force acts with respect to the electric charge induced in an object to be attracted, large electrostatic attractive force (Johnson-Rahbeck force) can be obtained without the need to form a thin dielectric layer.
However, the electrostatic chuck having a dielectric layer admixed with the conventional conductive ceramics is associated with the problem that if the chuck is used under severe conditions such as in a plasma environment, the electrical conductivity is liable to change, making the attractive force unstable.
This inconvenience can be mitigated to some extent by using a dielectric layer in which alumina is admixed with titania to make the titania deficient in oxygen and thereby increase the electrical conductivity. However, if an electrostatic chuck having such a dielectric layer is used in a plasma gas containing oxygen, the surface of the dielectric layer is oxidized, and since the electrical conductivity of the dielectric layer lowers, the attractive force of the electrostatic chuck decreases and also the attraction and release of a wafer slow down.
The present invention was created in view of the above circumstances, and an object thereof is to provide an electrically conductive ceramics whose electrical conductivity can be varied over a wide range and yet is reduced in variations, and a process of producing such a ceramics.
Another object of the present invention is to provide an electrically conductive ceramics which shows small change in electrical conductivity even in a severe atmosphere such as in a plasma environment or high-temperature oxidizing atmosphere and which can therefore be used stably, and a process of producing such a ceramics.
Still another object of the present invention is to provide an electrostatic chuck which shows small change in electrical conductivity and thus can produce large electrostatic attractive force even when used under severe conditions such as in a plasma environment.
Further object of the present invention is to provide an electrostatic chuck which shows small change in electrical conductivity and thus can produce large electrostatic attractive force even when used under severe conditions such as in a plasma environment containing oxygen.
According to a first aspect of the present invention, there is provided an electrically conductive ceramics comprising a compound containing at least one element belonging to the Group 3A of the periodic table, and TiO2xe2x88x92x (0 less than x less than 2), in a range such that the TiO2xe2x88x92x (0 less than x less than 2) accounts for 1 to 60 wt % of a total amount of the ceramics wherein at least part of the compound and the TiO2xe2x88x92x form a composite oxide.
According to a second aspect of the present invention, there is provided an electrically conductive ceramics comprising a compound containing at least one element belonging to the Group 3A of the periodic table, and TiO2xe2x88x92x (0 less than x less than 2), in a range such that the TiO2xe2x88x92x (0 less than x less than 2) accounts for 1 to 42 wt % of a total amount of the ceramics wherein at least part of the compound and the TiO2xe2x88x92x form a composite oxide.
According to a third aspect of the present invention, there is provided a process of producing an electrically conductive ceramics comprising the steps of: admixing powder of a compound containing at least one element belonging to the Group 3A of the periodic table, with powder of TiO2 or of a composite oxide consisting essentially of TiO2 and a compound containing at least one element belonging to the Group 3A of the periodic table, in a ratio such that the TiO2 accounts for 1 to 60 wt % of a total amount of the powder mixture; forming the powder mixture to obtain a formed body; sintering the formed article to obtain a sinterd body; and heating the sinterd body in an inert gas or in a reducing atmosphere at a temperature of 1300 to 1700xc2x0 C. with a surface of the sinterd body kept in contact with a substance containing carbon as a main component.
According to a fourth aspect of the present invention, there is provided an electrostatic chuck having an electrode and a dielectric layer formed on the electrode, for electrostatically attracting an object on the dielectric layer when voltage is applied to the electrode, wherein the dielectric layer is formed of a ceramics which comprising an oxide containing at least one element belonging to the Group 3A of the periodic table and TiO2xe2x88x92x (0 less than x less than 2) and in which at least part of the oxide and the TiO2xe2x88x92x form a composite oxide, and the dielectric layer has an electrical conductivity of 10xe2x88x928 to 10xe2x88x9214 S/cm.
According to a fifth aspect of the present invention, there is provided an electrostatic chuck having an electrode and a dielectric layer formed on the electrode, for electrostatically attracting an object on the dielectric layer when voltage is applied to the electrode, wherein the dielectric layer is formed of a ceramics which has electrical conductivity and which contains, as main components, an oxide containing an element belonging to the Group 3A of the periodic table and a composite oxide having oxygen deficiency and containing Ti and an element belonging to the Group 3A of the periodic table, and the electrical conductivity of the ceramics is 10xe2x88x928 to 10xe2x88x9214 S/cm.
According to a sixth aspect of the present invention, there is provided an electrostatic chuck having an electrode and a dielectric layer formed on the electrode, for electrostatically attracting an object on the dielectric layer when voltage is applied to the electrode, wherein the dielectric layer is made of a ceramics which has electrical conductivity and which contains, as main components, an oxide containing an element belonging to the Group 3A of the periodic table and a composite oxide having oxygen deficiency and containing Ti and an element belonging to the Group 3A of the periodic table, and the dielectric layer is obtained by the step of admixing powder of a compound of an element belonging to the Group 3A of the periodic table, with powder of a Ti compound or of a composite oxide containing Ti and an element belonging to the Group 3A of the periodic table, to obtain a powder mixture, the step of forming the powder mixture to obtain a formed body, the step of sintering the formed body in the air to obtain a sinterd body, and the step of heat-treating the sinterd body in a reducing atmosphere such that the dielectric layer obtained has an electrical conductivity of 10xe2x88x928 to 10xe2x88x9214 S/cm.
According to a seventh aspect of the present invention, there is provided an electrostatic chuck having an electrode and a dielectric layer formed on the electrode, for electrostatically attracting an object on the dielectric layer when voltage is applied to the electrode, wherein the dielectric layer is made of a ceramics which has electrical conductivity and which contains, as main components, an oxide containing an element belonging to the Group 3A of the periodic table and a composite oxide having oxygen deficiency and containing Ti and an element belonging to the Group 3A of the periodic table, and the dielectric layer is obtained by the step of admixing powder of a compound of an element belonging to the Group 3A of the periodic table, with powder of a Ti compound or of a composite oxide containing Ti and an element belonging to the Group 3A of the periodic table, to obtain a powder mixture, the step of forming the powder mixture to obtain a formed body, the step of sintering and simultaneously heat-treating the formed body in a reducing atmosphere, such that the dielectric layer obtained has an electrical conductivity of 10xe2x88x928 to 10xe2x88x9214 S/cm.
The present invention was created based on the below-mentioned findings of the inventors hereof.
(1) By admixing a compound containing at least one element belonging to the Group 3A of the periodic table with TiO2xe2x88x92x (0 less than x less than 2) and making at least part of the compound and the TiO2xe2x88x92x form a composite oxide, it is possible to obtain an electrically conductive ceramics of which the electrical conductivity can be varied over a wide range and yet is reduced in variations.
(2) By suitably controlling the content of TiO2xe2x88x92x (0 less than x less than 2), it is possible to obtain an electrically conductive ceramics which shows small change in electrical conductivity even in a severe atmosphere and thus can be stably used.
(3) By using such an electrically conductive ceramics as a dielectric layer and suitably controlling its electrical conductivity, it is possible to provide an electrostatic chuck of which the electrical conductivity of the dielectric layer undergoes little change even when used in a plasma environment, especially in a plasma gas containing oxygen, and which can stably produce large electrostatic attractive force by means of Johnson-Rahbeck force.